The exponential growth in the demand for wireless data communications has put tremendous pressure on cellular network operators to improve the capacity of their communication networks. To improve the spectral efficiency of these networks, scarce radio resources need to be reused aggressively in neighboring cells. As a result, inter-cell interference is a significant source of signal disturbance, limiting both the service quality of cell-edge users and overall system throughput.
Coordinated multi-point (CoMP) transmission or reception is one promising option because of its promise to effectively mitigate inter-cell interference. The idea behind CoMP in the downlink is to connect multiple remote base-stations via certain backhaul communication links from several adjacent cells to a central processor (CP) to form a “super-cell,” or a CoMP cluster, such that transmission to or reception from multiple user equipments (UEs) within each CoMP cluster can be coordinated by the central processor to reduce or even avoid mutual interference among UEs. The benefit attainable by the deployment of CoMP depends on how well that coordination can be performed by the CP.
To enable the central processor to effectively coordinate transmission and/or reception at multiple cells, signal information must be communicated between remote base station sites and CP in a timely fashion. But the amount of information that must be sent to or received from each remote site can be overwhelming, especially when multiple antennas are deployed at each site. For example, in the Common Public Radio Interface (CPRI), each real-valued sample of the IQ (complex-valued) backhaul signal is simply quantized independently by a fixed number of bits (e.g., 15 bits). It does not exploit any structure of the underlying backhaul signal and is an inefficient way of representing wireless communication signal. This puts an unnecessarily large burden on the capacity of backhaul links. What is needed is an effective method to compress those multi-antenna signals with both in-phase (I) and quadrature-phase (Q) components for each antenna branch.